Skin color is assessed using which of the following metrics?

Skin reflectance is the correct metric used to assess skin color. This method involves measuring the amount of light that is reflected off the skin's surface, which varies based on the skin's pigmentation. Melanin, the pigment responsible for skin color, affects how much light is absorbed versus reflected. By quantifying this reflectance, researchers can objectively analyze variations in skin color among different populations.

In contrast, skin hydration level primarily pertains to how much moisture is present in the skin, which can affect its appearance but does not directly assess color. Skin thickness describes the physical dimensions of the skin layers but does not provide information about pigmentation or color. Skin temperature is related to physiological functions and can vary based on factors like circulation or environmental conditions, but it does not relate specifically to skin color assessment. Thus, skin reflectance is the most appropriate measure for analyzing skin color.